scholarly journals A steady-state mechanism can account for the properties of inositol 2,4,5-trisphosphate-stimulated Ca2+ release from permeabilized L1210 cells

1993 ◽  
Vol 289 (3) ◽  
pp. 861-866 ◽  
Author(s):  
J W Loomis-Husselbee ◽  
A P Dawson
Keyword(s):  
Steady State ◽  
Small Proportion ◽  
Time Course ◽  
Initial Rate ◽  
Atpase Inhibitor ◽  
Efflux Rate ◽  
Rapid Phase ◽  
L1210 Cells ◽  
Low Concentrations ◽  
Stimulation Of

We have investigated the effects of sub-maximal Ins(2,4,5)P3 concentrations on the Ca2+ permeability of the residual undischarged Ca2+ stores in electroporated or digitonin-permeabilized L1210 cells by measuring Ca(2+)-efflux rate after addition of the ATPase inhibitor thapsigargin. Low concentrations of Ins(2,4,5)P3, causing rapid discharge of a small proportion of the releasable Ca2+, result in a substantial stimulation of Ca2+ efflux after thapsigargin addition. This indicates firstly that in the absence of thapsigargin there must have been a substantial, counterbalancing, increase in rate of Ca2+ pumping, and secondly that the increased Ca2+ permeability is more consistent with a steady state than with a quantal model of Ca2+ release. Similar increases in passive Ca2+ permeability are produced by addition of concentrations of ionomycin which produce equivalent changes in Ca2+ loading to those produced by Ins(2,4,5)P3, although the time course and initial rate of Ca2+ release are very much slower. In the presence of a Ca(2+)-buffering system, the time course of Ca2+ release by Ins(2,4,5)P3 becomes superimposable on that of ionomycin, indicating that the initial rapid phase of Ins(2,4,5)P3-stimulated Ca2+ is at least partially due to positive feedback from extravesicular Ca2+.

Reduction in postsynaptic inhibition during maintained electrical stimulation of different nerves in the cat hindlimb

1994 ◽  
Vol 71 (6) ◽  
pp. 2281-2293 ◽  
Author(s):  
C. J. Heckman ◽  
J. F. Miller ◽  
M. Munson ◽  
K. D. Paul ◽  
W. Z. Rymer
Keyword(s):  
Electrical Stimulation ◽  
Steady State ◽  
Time Course ◽  
Initial Period ◽  
Input Resistance ◽  
Medial Gastrocnemius ◽  
Rapid Phase ◽  
Afferent Pathways ◽  
Lateral Gastrocnemius ◽  
Stimulation Of

1. Steady-state postsynaptic potentials (PSPs) were generated by prolonged (approximately 1 s) high-frequency (100-200 Hz) electrical stimulation of nerves in the cat hindlimb. The characteristics of these steady-state PSPs were compared for two polysynaptic afferent pathways (ipsilateral cutaneous sural vs. contralateral peroneal nerves), two animal preparations (decerebrate vs. chloralose), and two motoneuron pools (medial gastrocnemius vs. lateral gastrocnemius-soleus). 2. PSPs from both nerves usually (36 of 51 cases) contained a mixture of depolarizing and hyperpolarizing components. In all 36 cases where the PSP contained a hyperpolarizing component, a consistent qualitative pattern emerged during prolonged stimulation: the hyperpolarization reached a peak approximately 20 ms after stimulation onset and then decayed with a biphasic time course that consisted of an initial rapid phase (20–40 ms) and a later slower phase (200–400 ms) before the steady-state value was reached. This pattern occurred regardless of the differences in polysynaptic afferent pathways, animal preparations, and motoneuron pools. 3. The consistency of this overall pattern was remarkable, given the existence of several quantitative differences among the PSPs. These differences include the following: hyperpolarizing components were least common in the sural and peroneal PSPs in the decerebrate preparation. And only these sural and peroneal PSPs tended to have prolonged afterpotentials after stimulus cessation. The steady-state sural PSPs in the decerebrate preparation tended to generate the largest PSPs and, moreover, these PSPs did not follow the overall trend of having a statistically significant relation between the amplitude of the initial hyperpolarization and the amount of its decay. Finally, transient sural PSPs in lateral gastrocnemius-soleus motoneurons in the decerebrate preparation tended to have the largest hyperpolarizations. 4. To determine whether the decay of the hyperpolarization and the subsequent dominance of depolarization was due to a decreased inhibition or an increased excitation, injected current pulses were utilized to measure the changes in the cell's input resistance during the course of the synaptic input. A strong decrease in input resistance accompanied the initial period of maximal hyperpolarization (50% with respect to the resting input resistance). Input resistance then returned toward resting values as hyperpolarization faded and depolarization became dominant. However, there remained a persistent decrease in input resistance during the final phase of the PSP that amounted to < 10% of the initial decrease. These findings indicated that much of the reduction in hyperpolarization reflected a progressive decrease in synaptic efficacy for the inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Gadolinium Reduces AMPA Receptor Desensitization and Deactivation in Hippocampal Neurons

2001 ◽  
Vol 86 (1) ◽  
pp. 173-182 ◽  
Author(s):  
Saobo Lei ◽  
John F. MacDonald
Keyword(s):  
Steady State ◽  
Ampa Receptor ◽  
Hippocampal Neurons ◽  
Time Course ◽  
Single Channel ◽  
Trivalent Cation ◽  
Receptor Desensitization ◽  
Whole Cell ◽  
Low Concentrations ◽  
Cultured Hippocampal Neurons

The actions of the trivalent cation Gd3+ on whole cell AMPA receptor-mediated currents were studied in isolated hippocampal neurons, in nucleated or outside-out patches taken from cultured hippocampal neurons, and on miniature excitatory postsynaptic currents (mEPSCs) recorded in cultured hippocampal neurons. Glutamate, AMPA, or kainate was employed to activate AMPA receptors. Applications of relatively low concentrations of Gd3+ (0.1–10 μM) substantially enhanced steady-state whole cell glutamate and kainate-evoked currents without altering peak currents, suggesting that desensitization was reduced. However, higher concentrations (>30 μM) depressed steady-state currents, indicating an underlying inhibition of channel activity. Lower concentrations of Gd3+also increased the potency of peak glutamate-evoked currents without altering that of steady-state currents. An ultrafast perfusion system and nucleated patches were then used to better resolve peak glutamate-evoked currents. Low concentrations of Gd3+ reduced peak currents, enhanced steady-state currents, and slowed the onset of desensitization, providing further evidence that this cation reduces desensitization. In the presence of cyclothiazide, a compound that blocks desensitization, a low concentration Gd3+ inhibited both peak and steady-state currents, indicating that Gd3+ both reduces desensitization and inhibits these currents. Gd3+ reduced the probability of channel opening at the peak of the currents but did not alter the single channel conductance calculated using nonstationary variance analysis. Recovery from desensitization was enhanced, and glutamate-evoked current activation and deactivation were slowed by Gd3+. The Gd3+-induced reduction in desensitization did not require the presence of the GluR2 subunit as this effect was seen in hippocampal neurons from GluR2 null-mutant mice. Gd3+ reduced the time course of decay of mEPSCs perhaps as a consequence of its slowing of AMPA receptor deactivation although an increase in the frequency of mEPSCs also suggested enhanced presynaptic release of transmitter. These results demonstrate that Gd3+ potently reduces AMPA receptor desensitization and mimics a number of the properties of the positive modulators of AMPA receptor desensitization such as cyclothiazide.

Synergism between ouabain and monensin in neurogenic responses of guinea-pig vas deferens

1988 ◽  
Vol 66 (5) ◽  
pp. 643-647 ◽  
Author(s):  
Takeshi Katsuragi ◽  
Lulu Kuratomi ◽  
Koji Miyamoto ◽  
Tatsuo Furukawa
Keyword(s):  
Guinea Pig ◽  
Time Course ◽  
Vas Deferens ◽  
Contractile Activity ◽  
Atpase Inhibitor ◽  
Exchange System ◽  
Deficient Medium ◽  
Small Contraction ◽  
Monensin A ◽  
Stimulation Of

Interrelations between ouabain, a Na+–K+ ATPase inhibitor, and monensin, a Na+ ionophore, on noradrenaline liberation and contractile activity were evaluated in the guinea-pig vas deferens. Monensin (1 μM) per se elicited a small contraction of the tissue. However, amplitude and time to the peak of large and sustained contractions evoked by 10 μM ouabain were potentiated and markedly shortened, respectively, by monensin. Contractions elicited by ouabain with or without monensin were prevented by 3 μM phentolamine or by pretreatment with reserpine. Contractions evoked by K+-free solution were augmented by monensin. In an HPLC study, noradrenaline outflow from the vas deferens was moderately and considerably increased by monensin (10 μM) and ouabain (100 μM), respectively. The ouabain-evoked output of noradrenaline was enhanced in the presence of monensin and the time course for maximum noradrenaline release was shortened, as was the contractile activity. This enhanced outflow after ouabain plus monensin was reserpine sensitive but not tetrodotoxin sensitive. Furthermore, this noradrenaline outflow was roughly halved in Na+-deficient medium, but was unaltered in Ca2+-free medium. These findings suggest that the synergistic effect of ouabain and monensin on noradrenaline liberation from the guinea-pig vas deferens may be due to an elevation of cytoplasmic Ca2+ concentrations, presumably resulting from a stimulation of intracellular Na+–Ca2+ exchange system, but not enhanced Ca2+ entry.

scholarly journals Uptake and metabolism of myo-inositol by L1210 leukaemia cells

1988 ◽  
Vol 254 (1) ◽  
pp. 95-100 ◽  
Author(s):  
J D Moyer ◽  
N Malinowski ◽  
E A Napier ◽  
J Strong
Keyword(s):  
Steady State ◽  
De Novo ◽  
Initial Rate ◽  
Geometric Isomer ◽  
Passive Diffusion ◽  
Concentration Addition ◽  
Free Medium ◽  
Extracellular Concentration ◽  
L1210 Cells ◽  
Uptake And Metabolism

The initial rate of uptake of [3H]myo-inositol by L1210 murine leukaemia cells is directly proportional to the extracellular concentration and unaffected by several analogues of myo-inositol even at millimolar concentrations. Scyllitol, a geometric isomer of myo-inositol, partially inhibited the uptake of myo-inositol (40% at 0.1 mM). A portion of the uptake of myo-inositol was not inhibited even at 5 mM-scyllitol. At steady-state the intracellular concentration of [3H]myo-inositol is directly proportional to the extracellular concentration. Addition of myo-inositol to medium does not enhance the growth of L1210 cells; these cells can maintain an extracellular concentration of 20 microM-myo-inositol even when grown in myo-inositol-free medium. Synthesis of myo-inositol from glucose by L1210 cells was demonstrated by use of [13C]glucose and m.s. L1210 cells maintain myo-inositol pools by a combination of synthesis de novo and uptake of exogenous myo-inositol by either passive diffusion or a low affinity carrier.

scholarly journals Evidence that lanthanum ions stimulate calcium inflow to isolated hepatocytes

1981 ◽  
Vol 200 (1) ◽  
pp. 109-114 ◽  
Author(s):  
J C Parker ◽  
G J Barritt
Keyword(s):  
Plasma Membrane ◽  
Steady State ◽  
Initial Rate ◽  
Compartmental Analysis ◽  
Isolated Hepatocytes ◽  
Lanthanum Ions ◽  
Isolated Liver Cells ◽  
Isolated Liver ◽  
Predominant Effect ◽  
Stimulation Of

LaCl3 stimulated the initial rate of 45Ca2+ exchange measured under steady-state conditions in isolated liver cells. Cu2+ greater than La3+ = Fe3+ greater than Fe2+ = Zn2+ greater Ni2+ greater than Mn2+ also stimulated 45Ca2+ exchange. Compartmental analysis of 45Ca2+-exchange curves obtained in the presence or absence of La3+, and in the presence or absence of adrenaline, showed that the predominant effect of La3+ is to stimulate the inflow of Ca2+ to the cell from the medium. No evidence for an inhibition of Ca2+ outflow from the cell was obtained. In the presence of La3+, adrenaline caused no further stimulation of Ca2+ inflow to the cell. In the absence of adrenaline, La3+ increased the uptake of Ca2+ (measured by atomic-absorption spectroscopy) by isolated hepatocytes incubated at 1 degree C. The proposal that La3+ stimulates Ca2+ inflow to the liver cell by inducing a conformational change in the Ca2+-inflow transporter of the plasma membrane is briefly discussed.

scholarly journals TIME COURSE AND QUANTUM EFFICIENCY OF PHOTOSYNTHESIS IN CHLORELLA

1953 ◽  
Vol 36 (4) ◽  
pp. 563-579 ◽  
Author(s):  
Frederick S. Brackett ◽  
Rodney A. Olson ◽  
Robert G. Crickard
Keyword(s):  
Steady State ◽  
Quantum Yield ◽  
Dark Adaptation ◽  
Time Course ◽  
Random Distribution ◽  
Initial Rate ◽  
Chlorophyll Concentration ◽  
Intermittent Light ◽  
Quantum Requirement ◽  
Different Cultures

1. Though the quantum yield remains constant for different samples of the same culture despite great changes in respiration due to dark adaptation, the quantum requirement for different cultures varies from 6.1 to 13.5 quanta per molecule of oxygen evolved (q/m). 2. This variation from one culture to another appears to depend upon chlorophyll concentration, though other paralleling factors cannot be ruled out. 3. Both chlorophyll concentration and quantum requirement show a random distribution. A statistical median for 50 cultures and 99 determinations gives q/m = 8.5 with a systematic uncertainty of perhaps 10 per cent. Since the variations are real, the median is regarded as less important than the lower limit approached (about q/m = 6). 4. Dark adaptation under aerobic conditions produces an initial photosynthetic rate of nearly zero. The immediate rise to steady state is somewhat logarithmic in character and may require over 3 minutes. 5. In intermittent light (of periods from 1 to 6 minutes) the induction observed in subsequent light periods starts from a finite initial rate and occupies a shorter time, often as little as 30 seconds. 6. The theoretical importance of aerobic induction is discussed. A chlorophyll cycle of two photochemical steps is found to satisfy most of the observed characteristics and to be compatible with an efficiency independent of intensity.

scholarly journals Simultaneous determination of the kinetics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men

2006 ◽  
Vol 290 (4) ◽  
pp. R1071-R1079 ◽  
Author(s):  
Frédéric Lador ◽  
Marcel Azabji Kenfack ◽  
Christian Moia ◽  
Michela Cautero ◽  
Denis R. Morel ◽  
...  
Keyword(s):  
Cardiac Output ◽  
Steady State ◽  
Phase I ◽  
Time Course ◽  
Hemoglobin Concentration ◽  
Two Phase ◽  
Rapid Phase ◽  
Steady State Method ◽  
Exercise Onset ◽  
Kinetics Of

We tested whether the kinetics of systemic O2 delivery (Q̇aO2) at exercise start was faster than that of lung O2 uptake (V̇o2), being dictated by that of cardiac output (Q̇), and whether changes in Q̇ would explain the postulated rapid phase of the V̇o2 increase. Simultaneous determinations of beat-by-beat (BBB) Q̇ and Q̇aO2, and breath-by-breath V̇o2 at the onset of constant load exercises at 50 and 100 W were obtained on six men (age 24.2 ± 3.2 years, maximal aerobic power 333 ± 61 W). V̇o2 was determined using Grønlund's algorithm. Q̇ was computed from BBB stroke volume (Qst, from arterial pulse pressure profiles) and heart rate ( fh, electrocardiograpy) and calibrated against a steady-state method. This, along with the time course of hemoglobin concentration and arterial O2 saturation (infrared oximetry) allowed computation of BBB Q̇aO2. The Q̇, Q̇aO2 and V̇o2 kinetics were analyzed with single and double exponential models. fh, Qst, Q̇, and V̇o2 increased upon exercise onset to reach a new steady state. The kinetics of Q̇aO2 had the same time constants as that of Q̇. The latter was twofold faster than that of V̇o2. The V̇o2 kinetics were faster than previously reported for muscle phosphocreatine decrease. Within a two-phase model, because of the Fick equation, the amplitude of phase I Q̇ changes fully explained the phase I of V̇o2 increase. We suggest that in unsteady states, lung V̇o2 is dissociated from muscle O2 consumption. The two components of Q̇ and Q̇aO2 kinetics may reflect vagal withdrawal and sympathetic activation.

Acid extrusion in S3 segment of rabbit proximal tubule. I. Effect of bilateral CO2/HCO3-

1995 ◽  
Vol 268 (2) ◽  
pp. F179-F192 ◽  
Author(s):  
L. K. Chen ◽  
W. F. Boron
Keyword(s):  
Steady State ◽  
Proximal Tubule ◽  
Initial Rate ◽  
Iodoacetic Acid ◽  
Buffering Power ◽  
Acid Load ◽  
S3 Segment ◽  
Series Of Experiments ◽  
Acid Extrusion ◽  
Stimulation Of

Monitoring the absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein, we studied intracellular pH (pHi) regulation in the isolated perfused S3 segment of rabbit proximal tubule. To explain a previous observation, that steady-state pHi is higher in the presence than in the absence of CO2/HCO3- (N. L. Nakhoul, L. K. Chen, and W. F. Boron. J. Gen. Physiol. 102: 1171-1205, 1993), we examined the effect of bilateral (i.e., luminal and basolateral) CO2/HCO3- on the acid extrusion processes responsible for recovery of pHi from acid loads. To compute fluxes from rates of pHi change, we determined the pHi dependence of intrinsic intracellular buffering power, which was approximately 50 mM/pH at pHi 6.5 and fell linearly to approximately 20 mM at pHi 7.4. In one series of experiments, we monitored the rate of pHi recovery from an acid load imposed by an NH4+/NH3 prepulse. Over a broad range of pHi values, total net acid extrusion was approximately four times higher in bilateral presence of CO2/HCO3- than in its absence. In a second group of experiments, which were designed to determine the effect of CO2/HCO3- on luminal Na+/H+ exchange, we monitored the rate of pHi recovery elicited by adding Na+ back to only the lumen, after first removing Na+ bilaterally. Initial rate of luminal Na(+)-dependent net acid extrusion in presence of CO2/HCO3- was approximately 229 microM/s (pHi 6.92), approximately 1.8 times higher than the flux of approximately 127 microM/s (P < 0.005) obtained in absence of CO2/HCO3- (pHi 6.66). CO2/HCO3- alkali-shifted the flux vs. pHi relationship by 0.3-0.4 pH units. In a final series of experiments, we examined the effect of CO2/HCO3- on the Na(+)-independent alkalinization that follows the rapid, initial acidification elicited by bilateral Na+ removal. In the presence of CO2/HCO3-, lag time for initiation of the Na(+)-independent alkalinization was only approximately 36 vs. approximately 211 s (P < 0.002) in absence of CO2/HCO3-. Also, Na(+)-independent net acid extrusion rate was approximately two to three times higher in presence than in absence of CO2/HCO3- at comparable pHi. This Na(+)-independent acid extrusion was insensitive to N-ethylmaleimide (2 mM), but was inhibited approximately 94% by efforts to deplete intracellular ATP (i.e., removal of glucose and amino acids, plus addition of 2 mM cyanide and 10 mM iodoacetic acid). Stimulation of luminal Na+/H+ exchange and Na(+)-independent acid extrusion appears to be the major, if not the entire, explanation for the higher steady-state pHi caused by bilateral addition of CO2/HCO3-.

Abstract 5385: Transport of Free Fatty Acids in Cardiac Myocytes is Mediated by a Plasma Membrane Pump as Revealed by Monitoring Cytoplasmic Unbound Free Fatty Acids

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Andrew N Carley ◽  
J P Kampf ◽  
Alan M Kleinfeld
Keyword(s):  
Fatty Acids ◽  
Plasma Membrane ◽  
Steady State ◽  
Free Fatty Acids ◽  
Cardiac Myocytes ◽  
Time Course ◽  
Plasma Membranes ◽  
Initial Rate ◽  
Ffa Metabolism ◽  
Ffa Transport

The transport of FFA across the plasma membrane represents one of the earliest points at which FFA metabolism can be controlled by cardiac myocytes. Using novel methods to measure the intracellular unbound concentration of FFA ([FFA i ]), the first direct measurements of FFA transport across cardiac plasma membranes have been performed in freshly isolated cardiac myoctyes. Measurements of the unbound concentrations of FFA (FFA u ) in the aqueous phase were performed using the fluorescent ratio probe ADIFAB. Cardiac myocytes were microinjected with ADIFAB, and the transport of oleate and palmitate was determined by monitoring [FFA i ] using fluorescence ratio microscopy. FFA influx was initiated by rapidly increasing the extracellular concentration of FFA u ([FFA o ]) using FFA-BSA complexes, which clamped [FFA o ] at fixed values. The time course of influx was monitored from the change in [FFA i ], which rose exponentially to a steady state level (k influx ~ 0.01 s −1 ). Once steady state was achieved, efflux was initiated by changing the extracellular media back to zero [FFA o ]. Efflux was monitored by the decrease in [FFA i ] which, like influx, revealed exponential behavior (k efflux ~ 0.02 s −1 ). At steady state [FFA i ] was greater than [FFA o ] by a factor of ~3.5, indicating that during influx FFA are pumped up a concentration gradient. Both the initial rate of transport and the gradient ([FFA i ] > [FFA o ]) revealed saturation with increasing [FFA o ]. The initial rate of influx saturated at [FFA o ] > 200 nM, while the [FFA i ] > [FFA o ] gradient was relatively constant (~ 3.5) but began to decrease and approached 1 at [FFA o ] > 200 nM. The efflux rate constant decreased for [FFA o ] > zero, suggesting that efflux may be regulated by a mechanism that senses the level of circulating FFA u . Our results indicate that the mechanism of FFA transport across cardiac myocytes is regulated by the plasma membrane and allows for the efficient storage and release of FFA from cardiac myocytes. We suggest that this mechanism involves an as yet unknown membrane protein pump which enables the cells to accumulate surprisingly high concentrations of FFA. The ability to measure [FFA i ] and the demonstration of efflux are significant steps in understanding cardiac FFA metabolism. This research has received full or partial funding support from the American Heart Association, AHA Western States Affiliate (California, Nevada & Utah).

cAMP-dependent reduction in membrane fluxes during relaxation of arterial smooth muscle

1984 ◽  
Vol 246 (2) ◽  
pp. H306-H311 ◽  
Author(s):  
A. W. Jones ◽  
D. B. Bylund ◽  
L. R. Forte
Keyword(s):  
Time Course ◽  
Myosin Light Chain ◽  
Receptor Occupancy ◽  
Rat Aorta ◽  
Camp Content ◽  
Primary Mechanism ◽  
Threefold Increase ◽  
Low Concentrations ◽  
K Transport ◽  
Stimulation Of

Forskolin, an activator of adenylate cyclase, inhibited contractures induced in rat aorta by norepinephrine (NE) and angiotensin II and by KCl depolarization. The concentration of forskolin required to inhibit NE-induced contractures was significantly lower than required to inhibit KCl-induced contractures (IC50 0.18 +/- 0.01 vs. 2.2 +/- 0.2 microM). Forskolin effectively relaxed NE-induced contractures when active Na+-K+ transport was inhibited. Stimulation of 42K and 36Cl effluxes by NE was inhibited by low concentrations of forskolin. The IC50 for forskolin inhibition of 42K efflux, 0.17 +/- 0.02 M, was similar to that for relaxation of NE contraction. The time course for forskolin-induced increases in adenosine 3',5'-cyclic monophosphate (cAMP) was consistent with that for forskolin-mediated relaxation and its maintenance. Fifty percent inhibition of both NE-induced contractures and NE-stimulated 42K effluxes occurred at levels of cAMP that were 1.4 times basal, and 90% inhibition of both processes was associated with a two to threefold increase in cAMP content. In sharp contrast, the level of tissue cAMP associated with inhibition of KCl contractures was 6-10 times higher than that associated with inhibition of NE-induced contractures. We postulate that cAMP-dependent regulation of membrane fluxes stimulated by receptor occupancy represents a primary mechanism for relaxation of a NE contracture, whereas the processes that regulate depolarization-dependent channels and the phosphorylation of myosin light chain kinase occur at much higher cAMP content and apparently function in a secondary capacity.

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